The invention concerns a method for synchronization of clock pulse devices, in particular for the purpose of a precise position determination of an object in a radio-based positioning system.
Measurement methods which are based on the TDOA (“Time Difference of Arrival”) principle are known according to FIG. 1. A transponder T to be localized thereby repeatedly emits a transponder signal TS at certain points in time. This transponder signal TS is then received at multiple M base stations whose positions are fixed and known. The M base stations BS1, BS2, . . . , BSM possess means to precisely determine the arrival point in time of the transponder signal TS. For calculation of the position of the transponder T, the delay difference t1−t2, t1−t3 or t2−t3 of the transponder signal TS between the transponder T and at least two base stations BS1 and BSM is evaluated. In order to be able to precisely measure the delay differences, it is necessary to let the clock pulse sources of the base stations BS to run synchronously among one another. For this, either a very elaborate real-time capable background network or highly-precise, long-term stable clocks is required.
Coded signals are typically used as a transponder signal TS, and the determination of the arrival point in time of the signal TS at the base stations BS ensues via a correlation with a signal known to the base station BS. Such a correlation is, however, very computation-intensive for broadband and radio-frequency signals. If the transponder T and base station BS participating in a measurement are not synchronized, this correlation must ensue continuously and in a real-time capable manner in each base station. This is, at present, only economically realizable for a limited bandwidth with digital circuits.
A method for synchronization of a transmitter station and a receiver station that communicate with one another via a radio interface is known from German Patent Document DE 101 57 931 A1 (“DE '931”), that discloses a system in which, in the transmitter station, a transmission signal is generated with a signal source and emitted via the radio interface and a corresponding reception signal is received in the receiver station by the radio interface and is evaluated using a receiver signal source signal from a signal source on the receiver side that is adapted to the sender-side signal source.
For up-to-date adaptation of the synchronization between a transmission signal and a reception signal, similar modulations are applied to the transmission signal and the reception signal and both are intermixed with one another. The mixed signal is subsequently analyzed with regard to a frequency detuning.